Defence from fighter boxing in the same place (5)
I believe the answer is:
alibi
'defence' is the definition.
(alibi is a kind of defence)
'fighter boxing in the same place' is the wordplay.
'fighter' becomes 'ali' (I have seen 'Old fighter' mean 'ali' so perhaps 'fighter' could also mean 'ali').
'boxing' is an insertion indicator ('box' can mean contain, as in to put in a box).
'in the same place' becomes 'ib' ('ib.' can be a synonym of 'in the same place').
'ali' placed around 'ib' is 'ALIBI'.
'from' acts as a link.
(Other definitions for alibi that I've seen before include "Legal defence proving innocence" , "Defence against accusation - was somewhere else" , "Defence that one was somewhere else at the time of a crime" , "Claim put to court" , "Pretext; court excuse" .)